95 z28 , t56 , 4.10 gears and I am using TunerproRT . I tried to change the drive shaft pulses per revolution it is currently set at 44.023 pulses per revolution. I have tried playing with different numbers but cant seem to get it to read a higher speed. Not sure what exactly to change but if I could alter the speed sensor signal I would verify and adjust with a GPS. It basically reads 35mph when I am going about 55mph. Any input might be helpful.